Design Of Electronic Stability Augmentation System For A Small-Size Helicopter UAV

Stability augmentation methods are needed to improve the steerability and antiinterference ability of a small-size unmanned helicopter. Compared with methods that utilize a complicate mechanical flybar and an electronic tail gyro, stability augmentation methods adopting an electronic stability augmentation system(ESAS) with the absence of flybar can effectively reduce mechanical malfunction, maintenance cost, and power loss.This article focuses on the design of ESAS. Firstly, an easy-to-analyze mathematical model of a small-size helicopter is derived using the mechanism modelling method in order to make reference for the design of ESAS. The model consists of some simplified submodels: rigidbody dynamics, main rotor flapping dynamics, flybar flapping dynamics, etc. Qualitative analysis on the working principles of Bell-Hiller system and tail gyro are made and the requirements of ESAS are presented. ESAS can be divided into two parts: yaw channel controller and roll-pitch channel controller. The basic algorithm of yaw channel controller is PI control. However, the same normal PI controller cannot produce good tracking responses to sudden-changing and slow-changing given signals simultaneously. To solve this problem, three optimizations of algorithm are proposed:(1)gain scheduling algorithm,(2)improved antiwindup algorithm, and(3)arranging transient process algorithm. The validity of the last two algorithms is proved through simulation. IMC design is performed to obtain the yaw channel’s PID parameters. Roll-pitch channel controller can be further divided into angular velocity control mode and attitude control mode. An angular velocity controller, Bell-Hiller controller, is designed based on the mathematical model of the Bell-Hiller system. The functions of the Bell-Hiller controller’s parameters are explored via simulation. Through the comparative simulation with the PI controller, the proposed Bell-Hiller controller is shown to have better transient response performance. The complementary filter algorithm for attitude estimation is derived, then a PD controller for attitude control is designed. Finally, the article introduces the experimental platform, and presents experimental data analysis and improvements that can be made for a better ESAS. The experimental data validates the proposed ESAS algorithm. The ESAS enriches the flight control system, and improves the small-size helicopter UAV platform.